counterterrorism center and nbc news justice correspondent pete williams. michael, let me ask you about the things we heard at the news conference. hundreds if not thousands of news photos and videos taken at the finish line yesterday, they're particularly interested in ones that were taken, obviously, during, right before and right after these bombs exploded. it seems like an incredible pain staking search, almost a need until a haystack. what in particular will they be looking for? >> well, it is a need until a haystack but at least now they have enough of the timeline to know the period during which they really want to dig in to this media video, photographs and the like. what they're probably going to be looking for is anyone who looks a little bit suspicious. frankly, they don't know what that is at this point and such pain staking work. a lot of what shows up on these photos and videos won't actually seem relevant until they get additional information from somewhere else and this will take hundreds and hundreds of man hours of pouring through this. wh